Waste material is a natural byproduct of steel making and other metallurgical processes, such as the refining of iron-bearing ores. Steel making processes employing either a basic oxygen furnace or an electric arc furnace typically use large amounts of scrap, much of which is galvanized. Thus, the waste produced includes a dust containing oxides of iron as well as oxides of impurities such as zinc, lead and cadmium.
Electric arc furnace dust has been declared hazardous due to the high levels of lead and cadmium oxides and must therefore be collected and reprocessed in order to protect the atmosphere and groundwater. Basic oxygen furnace dust has been or is expected to be declared hazardous under future environmental regulations. Because of the presence of zinc and lead oxides, attempts to reclaim the iron oxides directly for reuse have not proved to be practical. Various alternatives to the direct recovery of the iron oxides have been proposed. One such proposal is to pelletize moist dust and then subject it to a very high temperature for a short period of time to sinter the pellets and to volatize the impurities. The very high temperature partially melts the iron oxide which rapidly forms a glass-like material which when it cools fuses the pellets together. The resultant iron-oxide mass is difficult to reduce and recovery of impurities is relatively ineffective.
Similarly, the recovery of elemental iron from iron-bearing materials such as iron-bearing ores have presented many difficulties. Generally, natural ore fines are too course for pelletization and too fine for iron making processes using conventional technology. Accordingly, it will be appreciated that there is still a significant need for an improved process for treating metal oxide fines to recover elemental iron from iron-bearing materials including iron-bearing ores, steel mill waste and other metallurgical process waste.
For a more detailed discussion of various known processes and apparatus for metal oxide recovery reference is made to U.S. Pat. Nos. 5,186,741; 4,701,214; 4,251,267; 3,452,972 and 2,793,109 all of which are hereby fully incorporated by reference.
An object of the present invention is to provide a process for agglomerating a dry mixture of mill waste having metal oxides including iron oxides therein, and a carbonaceous material containing at least about 20 wt % volatile matter without the addition of a binder under conditions sufficient to mobilize volatile matter from the carbonaceous material to bond the dry mixture and form green compacts for recycling that is simple and economical. Yet another object of the present invention is to provide a process for treating metal oxide fines to recover iron from steel mill waste and other metallurgical process waste that is simple and economical.